Adaptive video slew rate for video delivery

Abstract

Systems and methods for adaptively adjusting a slew rate of a dejitter buffer in a remote device in a distributed access architecture. The slew rate may be adjusted based on measurements of a fullness state of a buffer made over time. The measurements may be used to calculate a frequency offset value between the rate at which data leaves the buffer relative to the rate at which data enters the buffer and/or used to calculate a current working depth of the buffer. The adaptive slew rate adjustments may be based on the frequency offset value and/or the current working depth.

The invention claimed is: 
     
       1. A remote device that receives packetized video data from a video core through a packet-switched network, the device comprising:
 a clock configured to operate in asynchronous mode; 
 a dejitter buffer that receives the video data from the packet-switched network and outputs the video data to at least one module that adjusts the video data before sending the video data in a downstream direction; 
 a processing device that applies a slew rate adjustment to the clock and the dejitter buffer, the slew rate adjustment varying over time based on a measured state of the dejitter buffer. 
 
     
     
       2. The remote device of  claim 1  comprising an RPD. 
     
     
       3. The remote device of  claim 1  comprising an RMD. 
     
     
       4. The remote device of  claim 1  where the slew rate adjustment is based on a frequency offset determined by measuring a fullness state of the dejitter buffer over time. 
     
     
       5. The remote device of  claim 4  where the slew rate adjustment is based on a measured current fullness state of the dejitter buffer. 
     
     
       6. The remote device of  claim 1  where the at least one module applies an offset value to a PCR value in the video data received from the packet switched network. 
     
     
       7. The remote device of  claim 6  where the offset values are accumulated to produce an accumulated offset value, the accumulated offset value used to selectively add and/or selectively drop packets. 
     
     
       8. The remote device of  claim 7  where the magnitude of the accumulated offset value is reduced whenever a packet is selectively dropped and/or added. 
     
     
       9. The remote device of  claim 1  where the slew rate adjustment eliminates a frequency offset by measuring a fullness state of the dejitter buffer repeatedly over time. 
     
     
       10. The remote device of  claim 9  where the dejitter buffer is recentered after the frequency offset is eliminated. 
     
     
       11. A method for determining timing values to apply to packetized video data received asynchronously from a video core through a packet-switched network, the method comprising:
 receiving the video data from the packet-switched network in a dejitter buffer according to a first time base and outputting the video data from the dejitter buffer according to a second time base and to at least one module that adds timing information to the video data before sending the video data in a downstream direction; 
 applying a slew rate adjustment to decrease a difference between the first time base and the second time base over an interval, the slew rate adjustment varying over time based on a measured state of the dejitter buffer. 
 
     
     
       12. The method of  claim 11  implemented in an RPD. 
     
     
       13. The method of  claim 11  implemented in an RMD. 
     
     
       14. The method of  claim 11  where the slew rate adjustment is based on a frequency offset determined by measuring a fullness state of the dejitter buffer over time. 
     
     
       15. The method of  claim 14  where the slew rate adjustment is based on a measured current fullness state of the dejitter buffer. 
     
     
       16. The method of  claim 11  where the at least one module applies an offset value to a PCR value in the video data received from the packet switched network. 
     
     
       17. The method of  claim 16  where the offset values are accumulated to produce an accumulated offset value, the accumulated offset value used to selectively add and/or selectively drop packets. 
     
     
       18. The method of  claim 17  where the magnitude of the accumulated offset value is reduced whenever a packet is selectively dropped and/or added. 
     
     
       19. The method of  claim 11  where the slew rate adjustment eliminates a frequency offset by measuring a fullness state of the dejitter buffer repeatedly over time. 
     
     
       20. The method of  claim 19  including the step of recentering the dejitter buffer after the frequency offset is eliminated.